An organic electroluminescence (EL) device has many attractive features as a display (multi-color emitting device) such as low consumption power, flatness, high-response speed, wide viewing angle or the like. As for an organic EL display using such an organic EL device, an all-deposition type display in which an emitting layer or the like are formed by depositing a low-molecular weight organic material has been put into practical use in a small-size display such as a mobile phone.
In an all-deposition type organic EL display, materials are not used efficiently. In addition, a vacuum system or a color-coding mask for a deposition layer is required for production, and hence, film formation for a large-sized screen is difficult, whereby it has a problem regarding a reduction in cost and an increase in size.
On the other hand, if a coating-type organic EL display in which an emitting layer or the like are formed by coating a high-molecular material by ink-jetting, nozzle printing, gravure printing or the like can be realized, there is a possibility that the above-mentioned problems associated with a deposition method can be solved (a display in FIG. 2, for example, HIL: hole-injection layer, IL: interlayer (hole-transporting layer), LEP: high-molecular emitting polymer, ETL: electron-transporting layer). However, a coating-type organic EL display has an insufficient luminous efficiency and a shorter lifetime as compared with an all-deposition type display. In particular, it has a serious problem in blue emission.
Patent Document 1 discloses a hybrid-type organic EL display which is a combination of a coating-type display which is inexpensive and enables the screen size to be increased and a high-performance deposition type display (FIG. 3).
The organic EL display shown in FIG. 3 is an organic EL display obtained by a method in which a red emitting layer and a green emitting layer (LEP) are separately provided by a coating method, and a blue emitting layer is allowed to be a common layer (Blue Common layer) by depositing a low-molecular material. The display shown in FIG. 3 can enhance the blue emission performance, and it is possible to reduce to color-coding steps from 3 to 2 steps. However, since a coating type hole-transporting layer (IL) is in contact with the anode side of the blue emitting layer, emission performance of blue color was not sufficient.
The display shown in FIG. 4 which is disclosed in Non-Patent Document 1 exhibits a significant improvement in blue emission performance due to the provision of a hybrid connecting layer (HCL) between the blue common layer as a deposition layer and a coating layer.
As the material of HCL, in order to improve the blue emitting performance, not only matching between the hole-injecting and transporting properties and the blue emitting layer, electron injecting and transporting properties to a red emitting layer and a green emitting layer formed by coating are required; in particular, when a red emitting layer and a green emitting layer formed by coating are phosphorescent layers, a higher triplet energy (T1) is also required in order to prevent diffusion of triplet energy. As the material for HCL, when a common hole-transporting material, a common electron-transporting material or a common high T1 material are respectively used singly, there is a problem that comprehensive improvement in performance or color reproducibility of an organic EL multi-color light-emitting device cannot be attained satisfactorily. That is, due to diffusion of triplet energy from the red emitting layer and the green emitting layer, the blue common layer emits light, whereby color mixing occurs.